'\" et
.TH PTHREAD_MUTEXATTR_GETROBUST "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
pthread_mutexattr_getrobust,
pthread_mutexattr_setrobust
\(em get and set the mutex robust attribute
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_mutexattr_getrobust(const pthread_mutexattr_t *restrict
    \fIattr\fP, int *restrict \fIrobust\fP);
int pthread_mutexattr_setrobust(pthread_mutexattr_t *\fIattr\fP,
    int \fIrobust\fP);
.fi
.SH DESCRIPTION
The
\fIpthread_mutexattr_getrobust\fR()
and
\fIpthread_mutexattr_setrobust\fR()
functions, respectively, shall get and set the mutex
.IR robust
attribute. This attribute is set in the
.IR robust
parameter. Valid values for
.IR robust
include:
.IP PTHREAD_MUTEX_STALLED 6
.br
No special actions are taken if the owner of the mutex is terminated
while holding the mutex lock. This can lead to deadlocks if no other
thread can unlock the mutex.
.br
This is the default value.
.IP PTHREAD_MUTEX_ROBUST 6
.br
If the process containing the owning thread of a robust mutex
terminates while holding the mutex lock, the next thread that acquires
the mutex shall be notified about the termination by the return value
.BR [EOWNERDEAD] 
from the locking function. If the owning thread of a robust mutex
terminates while holding the mutex lock, the next thread that attempts
to acquire the mutex may be notified about the termination by the
return value
.BR [EOWNERDEAD] .
The notified thread can then attempt to make the state protected
by the mutex consistent again, and if successful can mark the
mutex state as consistent by calling
\fIpthread_mutex_consistent\fR().
After a subsequent successful call to
\fIpthread_mutex_unlock\fR(),
the mutex lock shall be released and can be used normally by other
threads. If the mutex is unlocked without a call to
\fIpthread_mutex_consistent\fR(),
it shall be in a permanently unusable state and all attempts to lock
the mutex shall fail with the error
.BR [ENOTRECOVERABLE] .
The only permissible operation on such a mutex is
\fIpthread_mutex_destroy\fR().
.P
The behavior is undefined if the value specified by the
.IR attr
argument to
\fIpthread_mutexattr_getrobust\fR()
or
\fIpthread_mutexattr_setrobust\fR()
does not refer to an initialized mutex attributes object.
.SH "RETURN VALUE"
Upon successful completion, the
\fIpthread_mutexattr_getrobust\fR()
function shall return zero and store the value of the
.IR robust
attribute of
.IR attr
into the object referenced by the
.IR robust
parameter. Otherwise, an error value shall be returned to indicate the
error. If successful, the
\fIpthread_mutexattr_setrobust\fR()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_mutexattr_setrobust\fR()
function shall fail if:
.TP
.BR EINVAL
The value of
.IR robust
is invalid.
.P
These functions shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The actions required to make the state protected by the mutex
consistent again are solely dependent on the application. If it is not
possible to make the state of a mutex consistent, robust mutexes can be
used to notify this situation by calling
\fIpthread_mutex_unlock\fR()
without a prior call to
\fIpthread_mutex_consistent\fR().
.P
If the state is declared inconsistent by calling
\fIpthread_mutex_unlock\fR()
without a prior call to
\fIpthread_mutex_consistent\fR(),
a possible approach could be to destroy the mutex and then reinitialize
it. However, it should be noted that this is possible only in certain
situations where the state protected by the mutex has to be
reinitialized and coordination achieved with other threads blocked on
the mutex, because otherwise a call to a locking function with a
reference to a mutex object invalidated by a call to
\fIpthread_mutex_destroy\fR()
results in undefined behavior.
.SH RATIONALE
If an implementation detects that the value specified by the
.IR attr
argument to
\fIpthread_mutexattr_getrobust\fR()
or
\fIpthread_mutexattr_setrobust\fR()
does not refer to an initialized mutex attributes object, it is
recommended that the function should fail and report an
.BR [EINVAL] 
error.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIpthread_mutex_consistent\fR\^(\|)",
.IR "\fIpthread_mutex_destroy\fR\^(\|)",
.IR "\fIpthread_mutex_lock\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<pthread.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
